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1998 GMC Safari - heater/ac actuator question

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Dec 4, 2006, 7:24 PM

Post #1 of 4 (3566 views)
     1998 GMC Safari - heater/ac actuator question  

We just bought this van and have discovered that the air/heat only comes out the front vents and not to defrost or underneath the dash. We cannot choose where the flow of air (hot/cold) is directed. The switch that controls the blend of air (hot/cold) works fine, the speed switch to blow the air works as well, and the on/off part of the selector switch works fine too. My husband did a little research with the auto parts' store clerk and the research shows that it's an electric actuator not a vacuum-powered actuator for this van. Could the problem be the selector switch or is the problem in the actual actuator? If it's the actuator, how can my husband get to it to replace it or test it?

Any help or insights would be greatly appreciated!

Thanks!! :)

lablady and husband

Veteran / Moderator

Dec 5, 2006, 7:29 AM

Post #2 of 4 (3558 views)
     Re: 1998 GMC Safari - heater/ac actuator question [In reply to]  

The mode control or air distribution on this vehicle is a vacuum operated system not an electrical one.
Most times when there is a vacuum supply problem from the engine as in the black tubing from the engine to the heater controls becomes cracked or broken the heater system would default to the defrost mode.
With you saying that yours is always in the vent mode, could be a number of different things causing this.
The mode door maybe stuck in one position from something falling into the defroster vent.
The mode control selector is not directing vacuum to the proper actuator. Possibly one of the vacuum lines from the selector switch to an actuator is leaking vacuum.
Or a bad actuator and it cannot move the mode door.
As for who is or isn’t doing what to whom is anyone’s guess.
I’ve just looked through the different test procedures and I don’t have one for this scenario.
So all I can suggest is to get under the dash and check for vacuum supply; that the mode switch actually switches vacuum delivery to the different lines and that the actuators are actually moving the different doors.
Here is a couple of diagrams that may help as in location of the different colors of lines and to whom there connected.

Canadian "EH"

New User

May 11, 2012, 1:06 PM

Post #3 of 4 (2449 views)
     Re: 1998 GMC Safari - heater/ac actuator question [In reply to]  

Perhaps the Canadian model had the vacuum operation in 1998 but in the US, it is all electrical!

Hammer Time
Ultimate Carjunky / Moderator

May 11, 2012, 2:27 PM

Post #4 of 4 (2442 views)
     Re: 1998 GMC Safari - heater/ac actuator question [In reply to]  

After 6 years, nobody cares.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

1998 GMC Safari - heater/ac actuator question

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